Well we playtested the HB11 combat system in our session last Sunday, and I generally got a negative reaction from the players. We have been using the HnS combat system, and the general feeling was that this was no where near as good.
The players didn't mind the second roll for the critical, or the fact that a bad roll on the critical could make a good roll into a bad result, but they all thought that the damage throshold on the core charts was way too high. As an example the party's 7th level ranger was attacking a 5th level fighter who was wearing rigid leather. The fighter had a DB of 93 (reduced to 78 through the armour reduction rules) and was parrying with 30 of his OB for an adjusted total DB of 108. The ranger has to get an adjusted roll of 61 to do even 1 point of damage to the fighter. The same roll using HnS would be a 48 (cause the fighter would have an extra 15 DB) which would do a 10F, which is 17 hits(total), 1 round of stun and an MP of -10. The main thing my players like about the HnS system is that it makes combats generally quite fast so they can get on with the rest of the adventure. As it turned out this ended up being a quick combat anyhow, but only because the party's cleric rolled really well on her celestial ball and then really well again on the C holy crit which stunned both the bad guys for 6 rounds - effectively combat over.
Most of my group have played RM2 in the past, so they quite enjoyed the RM-style crit tables, but the overall feeling was that the tables need to start doing damage at a much lower level. However, I quite like the fumble charts and will probably use them rather than the ones from the core rules.
Hawk